# Metafor

ULiege - Aerospace & Mechanical Engineering

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doc:user:integration:scheme:dynimplexpl

# Dynamic implicit/explicit integration scheme

## Description

Can shift from implicit scheme to explicit scheme and reciprocally.

## Data set

### Old Metafor Version <= 2422

See dynamic implicit and explicit for a description of schemes and the definition of density and initial velocities.

In addition, parameters must be defined to handle the shift (Global Parameters [REMOVED]):

• MDE_SHIM : implicit scheme (= MDE_NDYN)
• MDE_SHEX : explicit scheme

Shifting can be done automatically or manually or both. Another application of this algorithm is to stabilize explicit steps.

### New Metafor Version > 2422

ti = IeTimeIntegration(metafor)
ti.setExplicitTimeIntegration(tiExp)
ti.setImplicitTimeIntegration(tiImp)
ti.setCurrentDynamicTimeIntegration(tiImp)

where tiExp and tiImp are the references towards the explicit and implicit time integration scheme respectively.

## Automatic Shift (method 1 or 2)

By default, the algorithm chooses the method based on an integration error, the time step and the machine time. The definition MDE_ICPU = 1 must be done (shift based on CPU time, otherwise dummy shift for the battery). The shift is done only if estimated and critical time steps are equal (to a safety factor). When shifting from an explicit alpha-generalized method, explicit time steps can be computed with a bifurcation radius equal to zero to increase numerical dissipation. The option is activated for method=1 but not for method=2 (see Implicit/explicit shift management).

## Manual Shift (method 3 or 4)

The user can impose shifts (see command .sie). When shifting from an explicit alpha-generalized method, explicit time steps can be computed with a bifurcation radius equal to zero to increase numerical dissipation. The option is activated for method=3 but not for method=4 (see Implicit/explicit shift management).

## Balancing

When shifting from explicit to implicit, the first implicit time step is computed based on an integration error (majored by a value equal to the maximal change of step times the explicit step) in automatic shift and is equal to this value (maximal change of step times the explicit step) in manual shift. In addition, the user can impose a number of implicit balancing time steps when shifting from explicit to implicit. An implicit balancing step is computed based on an explicit number of steps corresponding to the maximal change, justifying why this is an integer.

## Balancing all explicit time steps (method 5)

All the computation is done with explicit time steps (method5). All explicit maximal change of explicit steps are balanced by an implicit step.

## Implicit/explicit shift management

It is mandatory to instanciate the IeShifManager and then the parameters can adjusted if required :

  iesm = IeShiftManager(metafor)
iems.setIeShiftMethod(meth)
iesm.setNbOfBalanceSteps(nbbs)
iesm.setMaxStepIncrease(msin)
iesm.setAutomaticShiftSecurity(secu)
iesm.setCpuDependency(cpuDep)

^ Parameter ^ default ^ description ^

 meth = IESM_NOSHIFTMETHOD : no shift (default) = IESM_AUTOMATICSHIFTMETHODWITHDISS shift done automatically from integration error and CPU times (requires MDE_ICPU=1); when shifting to an implicit method, explicit time steps are computed with numerical dissipation = IESM_AUTOMATICSHIFTMETHOD : shift done automatically from integration error and CPU times (requires MDE_ICPU=1); when shifting to an implicit method, there is no explicit time steps computed with numerical dissipation = IESM_MANUALSHIFTMETHODWITHDISS : shift times are set with the command .sie (see below); when shifting to an implicit method, explicit time steps are computed with numerical dissipation = IESM_MANUALSHIFTMETHOD : shift times are set with the command .sie (see below); when shifting to an implicit method, there is no explicit time steps computed with numerical dissipation = IESM_BALANCEDEXPLICITMETHOD : every msin explicit steps, balanced is done with an implicit step to stabilize nonlinear computing nbbs 0 when shifting to implicit, is equal to the number of balancing steps msin 6 maximal change of the time step; this value is the ratio of the implicit step to the explicit step for a change to implicit or a balancing, so this is an integer secu 1.5 safety coefficient for automatic shift cpuDep False specify if the automatic criterion for shifting from one time integration to another depends on the User CPU time. (Metafor Version > 2422)

For manual shift, the user can set times at which method is changed. This is done with the commands:

  metafor.getIeShiftManager().pushTimeOfShiftingToExplicit(time)
metafor.getIeShiftManager().pushTimeOfShiftingToImplicit(time)

where

 time time at which the shift takes place